config: handle conditional include when $GIT_DIR is not set up

If setup_git_directory() and friends have not been called,
get_git_dir() (because of includeIf.gitdir:XXX) would lead to

    die("BUG: setup_git_env called without repository");

There are two cases when a config file could be read before $GIT_DIR
is located.

The first one is check_repository_format(), where we read just the one
file $GIT_DIR/config to check if we could understand this
repository. This case should be safe. We do not parse include
directives, which can only be triggered from git_config_with_options,
but setup code uses a lower-level function. The concerned variables
should never be hidden away behind includes anyway.

The second one is triggered in check_pager_config() when we're about
to run an external git command. We might be able to find $GIT_DIR in
this case, which is exactly what read_early_config() does (and also is
what check_pager_config() uses). Conditional includes and
get_git_dir() could be triggered by the first
git_config_with_options() call there, before discover_git_directory()
is used as a fallback $GIT_DIR detection.

Detect this special "early reading" case, pass down the $GIT_DIR,
either from previous setup or detected by discover_git_directory(),
and make conditional include use it.

Noticed-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -1887,6 +1887,7 @@ enum config_origin_type {
 
 struct config_options {
 	unsigned int respect_includes : 1;
+	const char *git_dir;
 };
 
 typedef int (*config_fn_t)(const char *, const char *, void *);

config.c

@@ -207,13 +207,22 @@ static int prepare_include_condition_pattern(struct strbuf *pat)
 	return prefix;
 }
 
-static int include_by_gitdir(const char *cond, size_t cond_len, int icase)
+static int include_by_gitdir(const struct config_options *opts,
+			     const char *cond, size_t cond_len, int icase)
 {
 	struct strbuf text = STRBUF_INIT;
 	struct strbuf pattern = STRBUF_INIT;
 	int ret = 0, prefix;
+	const char *git_dir;
 
-	strbuf_add_absolute_path(&text, get_git_dir());
+	if (opts->git_dir)
+		git_dir = opts->git_dir;
+	else if (have_git_dir())
+		git_dir = get_git_dir();
+	else
+		goto done;
+
+	strbuf_add_absolute_path(&text, git_dir);
 	strbuf_add(&pattern, cond, cond_len);
 	prefix = prepare_include_condition_pattern(&pattern);
 
@@ -242,13 +251,14 @@ done:
 	return ret;
 }
 
-static int include_condition_is_true(const char *cond, size_t cond_len)
+static int include_condition_is_true(const struct config_options *opts,
+				     const char *cond, size_t cond_len)
 {
 
 	if (skip_prefix_mem(cond, cond_len, "gitdir:", &cond, &cond_len))
-		return include_by_gitdir(cond, cond_len, 0);
+		return include_by_gitdir(opts, cond, cond_len, 0);
 	else if (skip_prefix_mem(cond, cond_len, "gitdir/i:", &cond, &cond_len))
-		return include_by_gitdir(cond, cond_len, 1);
+		return include_by_gitdir(opts, cond, cond_len, 1);
 
 	/* unknown conditionals are always false */
 	return 0;
@@ -273,7 +283,7 @@ int git_config_include(const char *var, const char *value, void *data)
 		ret = handle_path_include(value, inc);
 
 	if (!parse_config_key(var, "includeif", &cond, &cond_len, &key) &&
-	    (cond && include_condition_is_true(cond, cond_len)) &&
+	    (cond && include_condition_is_true(inc->opts, cond, cond_len)) &&
 	    !strcmp(key, "path"))
 		ret = handle_path_include(value, inc);
 
@@ -1603,10 +1613,12 @@ void read_early_config(config_fn_t cb, void *data)
 {
 	struct config_options opts = {0};
 	struct strbuf buf = STRBUF_INIT;
+	char *to_free = NULL;
 
 	opts.respect_includes = 1;
-	git_config_with_options(cb, data, NULL, &opts);
 
+	if (have_git_dir())
+		opts.git_dir = get_git_dir();
 	/*
 	 * When setup_git_directory() was not yet asked to discover the
 	 * GIT_DIR, we ask discover_git_directory() to figure out whether there
@@ -1615,7 +1627,12 @@ void read_early_config(config_fn_t cb, void *data)
 	 * notably, the current working directory is still the same after the
 	 * call).
 	 */
-	if (!have_git_dir() && discover_git_directory(&buf)) {
+	else if (discover_git_directory(&buf))
+		opts.git_dir = to_free = xstrdup(buf.buf);
+
+	git_config_with_options(cb, data, NULL, &opts);
+
+	if (!have_git_dir() && opts.git_dir) {
 		struct git_config_source repo_config;
 
 		memset(&repo_config, 0, sizeof(repo_config));
@@ -1624,6 +1641,7 @@ void read_early_config(config_fn_t cb, void *data)
 		git_config_with_options(cb, data, &repo_config, &opts);
 	}
 	strbuf_release(&buf);
+	free(to_free);
 }
 
 static void git_config_check_init(void);

t/t1305-config-include.sh

@@ -208,6 +208,17 @@ test_expect_success 'conditional include, both unanchored, icase' '
 	)
 '
 
+test_expect_success 'conditional include, early config reading' '
+	(
+		cd foo &&
+		echo "[includeIf \"gitdir:foo/\"]path=bar6" >>.git/config &&
+		echo "[test]six=6" >.git/bar6 &&
+		echo 6 >expect &&
+		test-config read_early_config test.six >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'include cycles are detected' '
 	cat >.gitconfig <<-\EOF &&
 	[test]value = gitconfig